The Internet of Things (IoT) paradigm aims to interconnect a variety of heterogeneous Smart Objects (e.g., sensors, smart devices, home automation equipment) using Machine-to-Machine communications. Smart mobile devices have become one of the primary ways for people to access entertainment and other business applications, both inside and outside of their homes. Location-based services are beginning to gain popularity with the increased use of smart mobile devices. Fast and energy-efficient indoor localization systems may require specialized hardware and RF signals or beacons to achieve accuracy and demand additional infrastructure and meticulous engineering for efficient working. Current indoor localization systems require extensive calibration and practical deployment overhead. Additionally, Wi-Fi signals used in these systems are more prone to multi-path and fading effects from static objects and human movement. Moreover, accelerometers inside smart mobile devices used to predict user location suffer from high battery energy consumption. An energy-efficient indoor localization system is desired.